1. Field of the Invention
The present invention relates to a random data generator, and more particularly, to a digital frequency jittering circuit that utilizes the random data generator for varying a switching frequency of a power supply, and a related method thereof.
2. Description of the Prior Art
A primary problem that plagues a conventional switching power supply is the electromagnetic interference (EMI) effect. It is well known that the EMI generated by the switching power supply can cause problems for communications devices in the vicinity of the power supply. Additionally, the high frequency signal of EMI will be coupled to a component of the AC mains signal that will be provided to other devices. Furthermore, the radiated EMI by the power supply can interfere with wireless radio and wireless television transmissions that are carried by other entities. It is well known that to reduce the negative effects of the electromagnetic interference (EMI) of a switching power supply one can scatter the power of a predetermined frequency by utilizing a prior art frequency jittering means. The effect of the scattered power depends upon the range that the predetermined frequency to be scattered within an operating frequency range. For instance, a wider irregular range of the predetermined frequency to be scattered within the operating frequency range results in a smaller EMI being generated in the switching power supply. In other words, when the power is distributed over the wider frequency range, the EMI effect is alleviated. Therefore, generating the irregular scattered range of the predetermined frequency within the operating frequency range is a critical factor in lowering the effect of the EMI of the switching power supply.
Please refer to FIG. 1. FIG. 1 illustrates a prior art frequency jittering generator 10. The frequency jittering generator 10 utilizes a state transition logic circuit 12 to generate a pseudo random value. Thepseudo random value is then transmitted to an output logic circuit 14 to generate an output signal, and the output signal is then sampled by a sampling unit 16 that is controlled by a clock signal. An output logic circuit 14 will generate a group of binary output signals for being converting into an oscillating signal with a frequency that corresponds to the group of binary output signals by utilizing a digital to frequency converter 18. Because state transition logic circuit 12 is derived from a predetermined rational equation, and the predetermined rational equation will generate a sequential output as the random value, the oscillating signal that is obtained from the sampled binary output signal is a regulated sequential jittering signal in a long term. Accordingly, the frequency jittering generator 10 does not effectively overcome the EMI effect of the switching power supply.
It is apparent that new and improves methods and devices are needed to solve the above-mentioned problems.